Cystic Fibrosis (CF) Carrier Screen
Inherited Genetic Disorders
When a couple is considering having a baby, there are certain factors that may add extra weight to the decision. One such factor is inherited genetic disorders, such as cystic fibrosis, sickle cell disease, thalassernia, and Tay-Sachs disease. What these diseases have in common is that they are passed on through carriers who may not have the disease themselves, but carry a genetic mutation of the gene that can cause the disease in their children.
Cystic Fibrosis Carriers
Cystic fibrosis (CF), like Tay-Sachs disease and the others, is a recessive disorder. That means that a person must inherit a defective gene from each parent in order to have the disease. A carrier of a defective gene for cystic fibrosis has one normal copy of the gene from one parent and a defective copy from the other parent. Usually, carriers of a recessive disorder do not have the disease themselves.
If only one parent in the couple is a CF carrier, none of the children will have CF. However, there's a 50 percent chance that each child will, in turn also be a symptomless carrier of CF. If both parents are carriers of the defective gene, then there's a 25 percent chance their baby will inherit one defective gene from each parent and have the disease. There's a 50 percent chance the child will be a carrier and there a 25 percent chance the baby will not have the gene at all.
Cystic Fibrosis - The Disease
Cystic fibrosis is an inherited disease that affects breathing and digestion. It is estimated that 30,000 children and adults in the US have the disorder. It is caused by an abnormal gene involved in mucus production in the body. The buildup of mucus in the lungs promotes chronic infections and ultimately loss of lung function. The thick mucus blocks the pancreas stopping digestive enzymes from reaching the intestines so serious problems arise from poor food absorption. The mucus can block the bile duct in the liver - a situation that causes permanent damage in about six percent of those with CF. The ability to have children affects most men with CF. Because of improved medical treatments and care, nearly half the CF patients today are 18 years-of-age or older. Many people with cystic fibrosis live well into their 30s, 40s, and beyond.
Screening is done through a process of determining risk factors. In the preconception visit or first prenatal examination the medical practitioner will ask questions about the risk of inherited genetic disorders in the family. If either partner has a family history of CF or is at high risk of being a carrier, the practitioner will likely order a screening to determine the risk.
The CF carrier screen test is either a saliva or blood test taken by parents to see if they carry the abnormal genes that cause CF, in order to determine the risk of having a child with CF. If the test results show that both parents are CF carriers, the health care provider can test the baby in-utero. If the baby has CF, parents can take time before delivery to learn more about the disease and find appropriate specialists.
CF carrier screening does not provide a diagnosis. As with all screenings, it indicates the risk and probabilities for the disease. The test to diagnose CF is the sweat test, considered to be the gold standard in diagnosing CF. The sweat test measures the amount of chloride in the sweat. It is not invasive - no needles are used in this test. Instead, a chemical that causes sweating is put on a small area of the arm or leg. An electrode is used to apply a weak electrical current to the area to cause sweating. The sweat is gathered and sent off for measurement of chloride in the sweat.
Although screening is optional in most cases, if there is any chance either partner is at risk of being a carrier, having the necessary tests can make a big difference in the decision making process.
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